1. Field of the Invention
The present invention relates to an electronic package assembly. In particular to a socket that utilizes EMC fingers for coupling a heat sink to the ground plane of a printed circuit card or planar using an integrated circuit socket.
2. Description of the Prior Art
Present day Integrated Circuit (IC) components are becoming more integrated and more complex. There has been a steady progression toward larger IC devices to permit inclusion of a greater number of functions on the device. The result is that the heat produced by these larger semiconductor devices is not adequately removed by either natural air convection nor by powered ventilation, such as a fan. Furthermore, clock frequencies and power generation constantly increase required electromagnetic shielding to prevent ElectroMagnetic Interference (EMI) with other devices. Microprocessors and microcontrollers being cases in point.
Convection cooling is performed by use of a heat sink that is directly applied to the device. It is not desirable to use a bonding process, such as an adhesive, because of the permanent nature of such attachment; a chip may be discarded if malfunctioning and it is not desirable to throw away the heat sink too. It has therefore been found desirable to attach the heat sink to the chip by mechanical means such as a retainer clip. The typical heat sink currently in use comprises a flat plate, generally of the same size as the device, with a plurality of radiation fins extending upwardly. The heat sink is commonly fabricated from aluminum and is extruded and subsequently machined. The heat sink can also be used in conjunction with a fan to obtain forced convection.
A parallel development in the electronic assembly art has been the provision of means for detachably securing large and generally expensive IC devices to a printed circuit board. The industry has developed sockets for this purpose. The socket is permanently attached to the board through soldering of a plurality of downwardly extending contact pins. The socket body includes an identical layout of holes into which the device may be inserted and then detachably locked into position. The socket is generally the same size as the device. It is highly desirable in electronic assemblies to achieve a commonality of parts from numerous suppliers so that the assembly company may select from multiple sources. Sockets for semiconductor devices are typically standardized for various chips and/or chip families.
When heat sinks are used to remove heat from electronic devices (e.g., microprocessor or microcontroller) the close proximity of the heat sink and electronic device permits electromagnetic energy to couple from the electronic device to the heat sink. The heat sink acts as an antenna for the electronic device. This energy radiates from the heat sink and may even be amplified by the heat sink which leads to undesirable EMI which can cause problems for other devices in the vicinity of the electronic device. This radiated energy may also lead to EMI readings which are unacceptable to the regulatory authority of a host country (e.g., in the United States the FCC).
One prior art solution included using a low EMC microprocessor. This of course is undesirable because lower EMC usually corresponds to slower processing speed and less processing power. Another prior art solution entails securing one or more grounding braids from the heat sink to the planar or printed circuit board (PCB) with screws or the like. This solution requires more space on the planar to secure the braids, costly extra parts (e.g.,the braids and the screws), additional manufacturing steps to attach and secure the braids, and inhibits easy removal of the electronic device. Another prior art solution is depicted in U.S. Pat. No. 5,541,811 entitled "Shielding and Cooling Arrangement". This prior art solution uses a shielding hood that completely covers the semiconductor device and requires more space on the planar then the socket and semiconductor device. With this solution it is more difficult to remove and access the electronic device. This solution also requires installation of, separate hook fasteners on the planar which requires additional manufacturing steps and additional assembly operations.
These unresolved problems and deficiencies are clearly felt in the art and are solved by the invention in the manner described below.